In computer operation, it is often desirable to utilize modems, which allow a computer to send and receive data across conventional telephone lines. As known in the art, and to most users of computers, modems (a contraction for modulator/demodulator) are devices which convert digital signals from a computer or terminal into a modulated signal appropriate for transmission across conventional telephone lines. Most modems use a modulation technique which is appropriate for transmission over the relatively narrow usable band width of conventional phone lines.
For many years the mounting of electrical equipment such as modems on supporting frames commonly referred to as racks, has been a popular way of housing the equipment for good ventilation, access to circuitry, assistance in the rapid changing of sub-assemblies, and generally convenient use. Typically the racks include a single cavity which includes a plurality of slots into which the equipment may be inserted. For example, in the United States, the electronic industry association's standard nineteen inch-wide rack configuration has been in use in hundreds of thousands of installations, both laboratory and commercial. Other racks known as "card cages", used for many years in telephony and more recently with respect to computing equipment, have become important means for providing rack mounting. Card cages are known in the art as box-like structures which have guide slots (typically two cofacing slots) for holding the edges of a plurality of circuit boards, also known in the art as "cards" which normally slide in from the front of the cage and have connectors on the rear edges of the circuit boards which mate with compatible connectors permanently attached to the back of the rack or a back plane within the card cage. Most card cages have tended to be open, and relied on either natural convection, or forced convection through ventilation fans.
More recently, racks have been equipped with integral components such as AC outlet strips, ventilation fans and internal power supplies and have employed in a variety of applications. However, for the most part, the use of such rack mounted equipment has been limited to laboratories or technical equipment rooms because it is generally considered to be aesthetically unappealing and thus unacceptable for use in office areas or other professional sites.
In configurations such as racks which require careful construction and assembly in order to provide precise interaction between various elements, a main concern is that of manufacturing and assembly tolerances. Should a device not be manufactured or assembled as required, the device may not operate in the intended manner or may be damaged even by proper handling or operation. In configurations such as electrical component racks as described above which require circuit board enclosures to be slid into various slots resulting in an electrical connection, such assembly concerns are amplified. Not only is there a concern that the connections are made along the desired axis of connection to avoid damage due to pin misalignment or the like, but the connectors must be fully engaged along their axis of engagement, in order to assure optimum and reliable electrical transmission. Once again this concern is paramount when the devices may be used by unskilled or careless personnel.
As the circuitry used to operate modem circuit board circuitry must operate on voltages differing from 120 or 220 volts AC, it is at times necessary to provide voltage convertors or "power supplies" as referred to in the art, for converting such higher voltages to the desired lower operating voltages for operation of the modems. Due to efficiency limitations inherent in such converters, some electrical energy is lost as heat during the voltage conversion process. In order to prevent damage to such units due to overheating, it may advantageous to provide a "heat sink", to allow heat to be transferred from the power supply.
Heat sinks are known in the art as means for facilitating the transfer of heat away from a particular "hot" object, such as a resister or coils from a power supply. By providing a low path of thermal resistance between the heat sink and the hot object (such as direct contact), heat may be transferred to the heat sink, and transferred therefrom by other means known in the art.
One means for providing a heat sink in apparatuses which include framing members is to attach the item to be cooled to one of the framing members, thus allowing the framing member to act as a heat sink. However, to assure the transfer of heat it is important that sufficient contact be made between the object to be cooled and the heat sink. Such contact is normally done by providing fasteners such as machine screws or rivets to rigidly and securely fasten the two members, thus providing the desired intimacy of contact between the two members.
The disadvantage of such connections is that they do not provide for a simple "quick-disconnect" configuration which may be desired if the connection is one that must be made repeatedly (such as is the case for interchangeable configurations) or must be made by unskilled personnel.
As discussed above with respect to power supplies, a need is also recognized in the art to provide cooling ventilation for circuit board assemblies, namely the components mounted on such circuit boards. This is especially the case for boards having a high resistor population, as in these components energy is necessarily converted from electrical energy to thermal energy. Therefore, a need is recognized in the art to provide means for cooling circuit boards. In order to prevent such overheating, prior art rack mount arrangements have provided for ventilation by natural convection, by leaving the racks relatively exposed to the operating atmosphere, or have provided forced convection ventilation by the use of one or more fans to draw air in from a normally open bottom or other opening through the entire cavity enclosed by the rack assembly.
However, such configurations have tendencies to draw ultimately large volumes of air through open unpopulated portions of the card cage, sometimes at the expense of adequate air flow over the boards in the populated portions of the cage. This has normally not been a problem in the prior art because the card cages have tended to be unenclosed circuit boards that allow adequate air to flow over the components even under widely varying conditions of the percent of the circuit card slots which are populated. However, this may be a problem when it is desired to use enclosed circuit boards within the cage, as such enclosed circuit boards necessarily introduce obstructions in the path of the ventilating air.
Therefore it may be seen that there is a need for an improved rack configuration for mounting multiple circuit boards. There is a particular need for such a unit which incorporates improvements in heat sinking, adjustability, and ventilation.